Finit is a small SysV init replacement with process supervision similar to that of daemontools and runit. Its focus is on small and embedded GNU/Linux systems, although it is fully functional on standard server and desktop installations. Finit is fast because it starts services in parallel; it then supervises and automatically restarts them if they fail. This can be extended upon with custom callbacks for all services, hooks into the boot process, or plugins to extend the functionality and adapt Finit to your needs. Finit is not only fast, it’s arguably one of the easiest to get started with. A complete system can be booted with one simple configuration file.

systemd is a system and service manager for Linux, compatible with SysV and LSB init scripts. It provides aggressive parallelization capabilities, uses socket and D-Bus activation for starting services, offers on-demand starting of daemons, keeps track of processes using Linux cgroups, supports snapshotting and restoring of the system state, maintains mount and automount points, and implements an elaborate transactional dependency-based service control logic. It can work as a drop-in replacement for sysvinit.

s6 is a complete process supervision suite in the style of daemontools, runit, and perp. It provides a candidate for process 1. It also comes with a library and command line utilities that implement inter-process notification and synchronization.

runonce is an attempt to take some of the pain out of postinstalls by moving them to the first boot of the system. This reduces the amount of items you have to worry about. If the postinstall script runs on a regular system, it should run on your postinstall.

iPXE is a network boot firmware. It provides a full PXE implementation enhanced with additional features such as the ability to boot from a Web server using HTTP, and the ability to boot from a SAN using iSCSI, AoE, SRP, or FCoE. It supports a wide variety of network devices, including wireless and Infiniband networks. iPXE is an effective replacement for gPXE.

Choose-OS (chos) is a minimalistic, fast, and
simple 2nd-stage boot loader for the Linux kernel
that works as an alternative to LILO. It is fully
configurable and supports, initrd, emergency boot,
a simple boot-time menu, hot-keys, timed boot, and
many other features.